1. Field of Invention
The present invention relates to a plasma display device known as a thin and light display device having a large screen.
2. Description of the Related Art
Recently, large size image display devices such as a plasma display device have been popularized. Such a large size image display device can clearly display an image in detail. On the other hand, in such a device, image turbulence, which is caused by an unstable supply of voltage from a power supply, tends to be noticeable. In order to avoid such a problem, it is important for a power supply unit of the image display device to keep an output voltage constant.
A plasma display device displays an image by performing a discharge in a large number of discharge cells provided in a plasma display panel (hereinafter, abbreviated as “PDP”). A discharge current of a PDP at this time is much dependent upon a gradation value of an image to be displayed. When the gradation value is increased, the discharge current of the PDP is increased. On the contrary, the gradation value is reduced, the discharge current is reduced.
Japanese Patent Unexamined Publication No. 2002-351379 (hereinafter, referred to as “patent document 1”) discloses an example of a power supply unit of a plasma display device in which an output voltage is made to be kept constant with respect to the above-mentioned change of a discharge current. This power supply unit detects a change of the output voltage generated when the discharge current is changed and carries out feedback control so that the output voltage becomes constant.
However, the power supply unit described in patent document 1 detects the change of the output voltage and thereafter carries out control for returning the voltage to the original voltage. Therefore, when the discharge current is significantly changed in a rapid manner, it is difficult to keep the output voltage constant.